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Some Further Thoughts on Arctodus

As you may remember from a little while ago i didn’t have the best outlook on everyone’s favorite ice age bruin Arctodus. The loss of what may have been one of the most fascinating carnivores of the Pleistocene is probably easier to bear (no pun intended) than i made it out to be. i have tried to make it clear that i have a mental illness that severely affects my outlook and disposition. However, looking back i now realize that Arctodus may be down, but he may not be out just yet.

A jawbone of Arctodus from Labor of Love Cave, Nevada

I talked about Arctodus being shrunk down from the giant it is often portrayed as. Well being the numb-nuts that i am, i had forgotten that the paper that stripped Arctodus of most of it’s unique characteristics actually argues that Arctodus may have been bigger than what some have argued:

According to our estimates,
the heaviest specimens of A. simus are UVP 015 from Utah and F:AM 25535 from Nebraska, with body masses calculated as ca. 957 and 863 kg, respectively (Table 3). In contrast, the smallest
specimens are LACM 122434 from Rancho La Brea and UM25611 from Kansas, with figures of ca. 317 and 388 kg, respectively (Table 3). The fact that one third of the specimens analyzed approached a ton suggests that individuals of this size were more common than previously suspected.

They go on to mention that the largest specimens come from colder climates (at least back then). This is consistent with what is observed in other mammals, in that cold climates favor larger body size. Also Arctodus appears to exhibit sexual dimorphism like modern bears, meaning that smaller specimens are most likely females. Another interesting note about the size of Arctodus comes from Riverbluff Cave in Missouri. Preserved on the walls of the cave are many parallel gouges consistent with claw marks. Based on the size and spacing of the marks they are thought to have been made by Arctodus. Another they think it’s Arctodus is that these claw marks are 12 feet up the cave wall! Finally, Eric Scott of the San Bernardino County Museum has offered to help quell my doubts by showing me an Arctodus astragalus from Murrieta and comparing it with other bears. There’s a field trip in May so I’ll try to to it then (Thanks Eric!).

And as for meat consumption… Well, the isotope analysis was performed on specimens from Alaska and hence can’t be used to generalize the species. But just like we can’t generalize from a few specimens, can we really generalize based on one paper? They have put forward the argument that Arctodus was an omnivore, but it should not be accepted as gospel truth. People argued for Arctodus being herbivorous based on anatomy, and look what happened: specimens were found that demonstrated a diet almost entirely of meat. It’s clear that Arctodus’ diet is a bit more complicated. Who knows, maybe Arctodus was an omnivore but was more carnivorous than modern bears (like, say, 30% meat 70% plants, or maybe 40%/60%). Arctodus being a primarily vegetarian animal like modern bears raises a question: if it was a generalist, why did it die out? Surely it could have adapted like it’s grizzly cousins. One of the reasons the scavenging hypothesis made sense to me was it could at least in part explain why Arctodus died out: If all the large animals that Arctodus relied on for carrion died out, then it too would die out from lack of food. Just an observation.

In short, we still have much to learn about this animal. The dearth of fossils discovered so far should make it obvious that this bear isn’t giving up it’s secrets easily. To give you an idea of how rare it’s fossils are, consider diamond Valley. Tens of thousands of fossils were found there during construction of a reservoir. Now predators make up as small part of the ecosystem, so they are less likely to be fossilized. But still, paleontologists in Diamond Valley found: a saber-toothed cat mandible and foot bone, a vertebra and pelvis of the American lion, and a cranium fragment, a foot bone, and tooth fragments of a dire wolf. What did they find of Arctodus? A single incisor! Of all the fossils found, the mighty Arctodus is represented by a single front tooth. Even in a predator trap like the La Brea Tar Pits, it’s a rare beats. Compare 30 bears to 3200 dire wolves, 2000 saber-toothed cats, and over 120 American lions. Not a whole lot to go on. I think we need to try and get a better idea of this bear’s biomechanics: how strong was it’s bite, how did move, how did its limbs function? Also i think we need to try and do isotope studies on fossils besides one found in the north. Perhaps diet may also explain why larger specimens are found in places like Utah and Nebraska. But we won’t know for sure until we focus on trying to figure this animal out rather than trying to bust popular myths.

I suspect these 19 feet estimates could be rather approximate, but I asked the photographer to confirm this size for me.

I reason thusly: If a modern Kodiak bear can stand 9-10 feet fully erect on average, and there have been historical records of 12 -14 feet “long” Kodiak specimens in the 1880’s shot and measured from nose to tail, it isn’t totally out of the realm to think “maybe” some Arctodus or similar sized bears which grew 11 to 13 feet “tall” (25% taller than Kodiak) on average, had on occasion exceptionally large males who grew 25% larger yet than the mean (that is to say, 15 -16 feet), and perhaps had a vertical arm reach of some 19 feet.

A 15 feet or taller bear is truly a scary prospect. I suspect they existed, if the claw marks were indeed 15 feet or greater above ground level, and with the law of averages suggesting that some individuals exceed by several deviations the average by so great as 25%, for instance a 7 feet 3 inch Basketball Center who is 25% taller than a standard 5 feet 10 inch European American male…